It's illegal for anyone to spray-paint city property, including companies and ad agencies.

So far, Levi's stenciled messages have been sighted in the Mission and the Castro.

This isn't the first time that companies have been caught sneaking around with graffiti. Last year, Microsoft tagged the city with spray-painted messages about some new software. The company claimed that the messages were chalk and would wash off with water, but they didn't.

More recently, Farmville maker Zynga glued slips of paper advertising a new game to city sidewalks.

Both companies were made to pay hefty fines and help the city clean up their mess. It's likely that the same fate await's Levi's. A representative City Attorney Dennis Herrera, a contender in the next mayoral race, has said via Twitter that he is already investigating.